At the Main Menu, head on over to the ‘Customisation’ section. From there, click on the ‘Car Liveries’ tab. Select ‘Create New’ to start customizing your own car, and gamers can choose from a variety of color schemes and designs, as well as sponsor decals that have been unlocked. You can also see which designs need to be unlocked, by the way, in the ‘Locked Items’ tab of the ‘Liveries’ section.
If you would like to edit your design after it is complete, hit the Edit button (X for Xbox One or PC) once you enter the livery menu and you will be able to do so. Just keep in this mind when you attempting to customize your car: the options that you have are limited to the pre-set options that are in the game. You can customize your car, but only as much as the game allows you to do so.